Correlation among Structure, Microstructure, and Electrochemical Properties of NiAl–CO3 Layered Double Hydroxide Thin Films

• Published in: Journal of physical chemistry. C Vol. 116; no. 29; pp. 15646 - 15659
• Main Authors: Faour, A, Mousty, C, Prevot, V, Devouard, B, De Roy, A, Bordet, P, Elkaim, E, Taviot-Gueho, C
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 26.07.2012
• Subjects: Chemical synthesis methods; Condensed Matter; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Growth from solutions; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Materials science; Methods of crystal growth; physics of crystal growth; Methods of nanofabrication; Nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals; Physics; Strongly Correlated Electrons; Structure of solids and liquids; crystallography; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Crystal growth; Rietveld method; Particle size; Spherical shape; Hydroxides; Polytypism; XRD; Glycine; Structural models; Thin films; Cyclic voltammetry; Trigonal lattices; Blood platelets; Size effect; Crystal growth from solutions; Pair distribution function; Double layers; Synchrotron radiation; Intergrowth; Domain growth; Spherical harmonics; Crystallinity; Allotropy; Hexagonal lattices; Electrochemical properties; Algorithms; Transmission electron microscopy; Hydrothermal synthesis; Anisotropy; Thin layer electrode; Coalescence; Microstructure; Electrochemical impedance spectroscopy; SUBSTITUTED NICKEL-HYDROXIDE; LDHS; ORDER; MODIFIED ELECTRODES; CRYSTALLINITY; STABILITY; DISORDER; PARTICLE-SIZE; AL; PAIR DISTRIBUTION FUNCTION
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp300780w

We studied a series of NiAl–CO3 layered double hydroxides (LDHs) of various degrees of crystallinity prepared by a glycine-assisted hydrothermal method. The structures and the microstructures were determined by Rietveld refinement with a spherical harmonic-implemented algorithm using high-resolution synchrotron powder X-ray diffraction (XRD) data. These XRD results combined with transmission electron microscopy (TEM) observations indicate that the broadening of 00l diffraction lines is mainly due to size effects, while both size and strain effects contribute to the anisotropic broadening of the other hkl reflections. The in-plane TEM dimensions of LDH platelets are found larger than the coherent lengths in the 110 direction, indicating a noncoherent coalescence of domains during crystal growth. The DIFFaX program was also used to model structural defects, i.e., CO3 2–/SO4 2– interstratification and intergrowth between rhombohedral 3R1 and hexagonal 2H1 polytypes. Furthermore, the distribution of the cations within the hydroxide layers has been determined by the atomic pair distribution function technique, indicating a disordered distribution of the cation in all samples with absolutely identical cationic coordination spheres. The electrochemical characterization of these samples as thin-film modified electrodes, by means of cyclic voltammetry and electrochemical impedance spectroscopy measurements, reveals complex behaviors which are the result of competing effects between the coherent domain size and the particle size, the aggregation state of LDH particles, the Ni bulk concentration, and the presence of structural defects. Remarkably, the presence of the 2H1 stacking motifs in the 3R1 LDH matrix results in an increased electrochemical signal. Either the location of metal cations exactly on top of the others in the 2H1 polytype or the defects associated with the intergrowth of 2H1–3R1 polytypes may be responsible for the enhanced electroactivity of Ni centers.